Clon is a library for managing command-line options in standalone Common Lisp applications. It provides a unified option syntax with both short and long names, automatic completion of partial names and automatic retrieval/conversion of option arguments from the command-line, associated environment variables, fallback or default values. Clon comes with a set of extensible option types (switches, paths, strings etc.). Clon also provides automatic generation and formatting of help strings, with support for highlighting on tty's through ISO/IEC 6429 SGR. This formatting is customizable through "themes".